Energy transfer between manganese(II) and thulium(III) in transition-metal fluoride glasses

Lead zinc gallium fluoride glass containing 2 mole% TmF₃ is shown to luminesce from ¹I₆ (35200 cm^?1), ¹D₂(28000), ¹G₄ (21500) and ³H₄ (12800) to several lower J levels. When the 24 mole% ZnF₂ is replaced by MnF₂ in the absence of thulium, the (broad band) quartet-to-sextet (ground state) emission at 16800cm^?1 has a mean lifetime of 1 ms. If 2 mole% TmF₃ is added to the latter glass, energy transfer decreases the lifetime to below 0.03 ms. The high critical radius R₀ (above 20 Å) is rationalized by Mn-Mn energy migration (concomitant with a lifetime shortened from 24 ms) to be compared with R₀≈ 8 Å for low Mn(II) concentration, almost identical with energy transfer between 1 mole% each of MnF₂ and NdF₃ previously studied in an analogous glass.